Peripheral artery disease (PAD) disproportionately affects the elderly. In its extreme form, PAD results in tissue ischemia, necrosis, ulceration and limb amputation in an already clinically compromised population. To date, however, no effective therapies exist for the treatment of PAD. Angiogenesis is the compensatory physiological response to tissue ischemia and occurs in PAD and other forms of cardiovascular disease. Interestingly, this seemingly protective angiogenic process is blunted in the elderly, and pharmacologic therapies aimed at augmenting the angiogenic response may prove effective. Tie2 and the Angiopoietins [unreadable] are essential components of embryonic and post-natal angiogenesis. Regulation of Tie2 signaling and [unreadable] function is complex, as its ligands, Angiopoietin-1 (Ang1) and Angiopoietin-2 (Ang2), have opposing effects on the vasculature. Ang1 promotes vascular maturation and stabilization while Ang2 promotes vessel destabilization, facilitating angiogenesis and vascular remodeling. Recent data from our group [unreadable] demonstrates the requirement of Tie2 signaling for exercise-induced angiogenesis in skeletal muscle, the same target tissue for therapeutic angiogenesis in PAD. Although naturally occurring hyperactivating mutants of Tie2 have been identified; they paradoxically result in altered vessel remodeling and vascular malformations as opposed to enhanced angiogenesis. Together, these observations implicate Tie2 as a potential pro-angiogenic therapeutic target and suggest a destabilizing role for the hyperactivating mutants during vascular remodeling, however little is known about alterations in Tie2 signaling pathways and downstream cellular responses that occur as a result of the activating mutations. We hypothesize that Tie2 signaling is required for ischemic angiogenesis and that Tie2 activating mutations disrupt vascular morphogenesis in part by activating signaling pathways and cellular responses necessary for vessel destabilization and vascular remodeling. Accordingly, the Specific Aims of this proposal are to: (1) Characterize the effects of the R849W activating mutation on Tie2 signaling (2) Characterize the effects of te R849W activating mutation on Tie2-mediated endothelial cellular responses (3)Determine the requirement forTie2 in ischemic angiogenesis and the age-dependent impairment of angiogenesis. [unreadable] [unreadable]